Vehicle behavior control device

ABSTRACT

There is provided a vehicle behavior control device capable of improving responsivity of a vehicle behavior and a linear feeling with respect to a steering wheel operation without causing a driver to experience a strong feeling of intervention of the control and, at the same time, capable of controlling behavior of a vehicle in such a manner as to also improve stability of the vehicle attitude and riding comfort. In a vehicle behavior control device applied to a vehicle  1  having steerable front road wheels  2 , the vehicle behavior control device includes a PCM  14  which acquires a steering speed of the vehicle, and increases a vertical load on the front road wheels when the steering speed becomes equal to or greater than a given threshold T S1  which is greater than zero.

TECHNICAL FIELD

The present invention relates to a vehicle behavior control device, andmore particularly to a vehicle behavior control device for controllingbehavior of a vehicle having steerable front road wheels.

BACKGROUND ART

Heretofore, there has been known a control system capable of, in asituation where behavior of a vehicle becomes unstable due to road wheelslip or the like, controlling the vehicle behavior to enable a safetraveling (e.g., an antiskid brake system). Specifically, there has beenknown a control system operable to detect the occurrence of vehicleundersteer or oversteer behavior during vehicle cornering or the like,and apply an appropriate degree of deceleration to one or more roadwheels so as to suppress such a behavior.

There has also been known a vehicle motion control device operable toautomatically perform an acceleration or a deceleration associated witha steering wheel operation which is started from a usual driving region,to thereby reduce skid in a marginal driving region, differently fromthe above control for improving safety in a traveling condition causingthe vehicle behavior to become unstable (see Patent Document 1, forexample).

CITATION LIST Patent Document

Patent Document 1: Japanese Patent No. 5193885

SUMMARY OF INVENTION Technical Problem

However, when the acceleration or the deceleration is automaticallycontrolled in response to an instruction from a control device as in thecase of the above-mentioned technique described in Patent Literature 1,the acceleration or the deceleration which does not necessarily agreewith the intention of a driver is performed and hence, the driver mayexperience a strong feeling of intervention of the control. On the otherhand, when control gain is reduced so as to suppress a feeling ofintervention of the control, advantageous effects which can be acquireddue to control of the acceleration or the deceleration are also reduced.

Further, the conventional technique described in Patent Literature 1focuses on that a driver performing only a steering operation forturning is allowed to realize a vehicle motion similar to the vehiclemotion of an expert driver. However, the conventional technique does notnecessarily acquire improvement in responsivity of vehicle behavior anda linear feeling with respect to a standard steering wheel operation.

The present invention has been made to solve the above conventionalproblem, and an object thereof is to provide a vehicle behavior controldevice capable of improving responsivity of vehicle behavior and alinear feeling with respect to a steering wheel operation withoutcausing a driver to experience a strong feeling of intervention of thecontrol and, at the same time, capable of controlling behavior of avehicle in such a manner as to also improve stability of the vehicleattitude and riding comfort.

Solution to Technical Problem

In order to achieve the above object, a vehicle behavior control deviceapplied to a vehicle having a steerable front road wheel, the vehiclebehavior control device including: a steering speed acquiring partconfigured to acquire a steering speed of the vehicle; and a verticalload increasing part configured to increase a vertical load on a frontroad wheel when the steering speed becomes equal to or greater than agiven threshold which is greater than zero.

In the present invention having such a configuration, the vertical loadincreasing part increases, when the steering speed becomes equal to orgreater than the threshold, a vertical load on the front road wheel andhence, after a driver starts the steering wheel operation, the verticalload on the front road wheel can be increased when an amount of lateralload shift of the front road wheel is increased in accordance with anincrease in lateral acceleration. With such a configuration, at theinitial stage of turning of the vehicle, the vertical load on the frontroad wheel is increased so as to suppress a decrease in vertical load onan inner front road wheel which is caused by a lateral load shift sothat a cornering force of the front road wheel is increased thusimproving responsivity of turning behavior. Therefore, it is possible toimprove responsivity of vehicle behavior and a linear feeling withrespect to the steering wheel operation without causing the driver toexperience a strong feeling of intervention of the control. Further,behavior which is intended by the driver is accurately realized andhence, extremely small correction steering becomes unnecessary thus alsoimproving stability of the vehicle attitude and riding comfort.

In the present invention, it is preferable that the vertical loadincreasing part is configured to start to reduce a driving force of thevehicle when the steering speed becomes equal to or greater than thethreshold, so as to increase the vertical load on the front road wheel.

In the present invention having such a configuration, after the driverstarts the steering wheel operation, a deceleration is generated in thevehicle by reducing the driving force, so that the vertical load on thefront road wheel can be increased with high responsivity. With such aconfiguration, at the initial stage of turning, the vertical load on thefront road wheel is promptly increased so as to suppress a decrease invertical load on the inner front road wheel which is caused by a lateralload shift so that a cornering force of the front road wheel isincreased thus improving responsivity of turning behavior.

In the present invention, it is preferable that, when the steering speedbecomes equal to or greater than the threshold, the vertical loadincreasing part is configure to increase the vertical load on the frontroad wheel, in synchronization with a lateral load shift of the frontroad wheel.

In the present invention having such a configuration, at the initialstage of turning of the vehicle, the vertical load on the front roadwheel can be increased such that a decrease in vertical load on theinner front road wheel which is caused by the lateral load shift isreliably suppressed. With such a configuration, a cornering force of thefront road wheel can be reliably increased and hence, responsivity ofturning behavior can be improved.

Effect of Invention

According to the vehicle behavior control device according to thepresent invention, it is possible to improve responsivity of vehiclebehavior and a linear feeling with respect to a steering wheel operationwithout causing a driver to experience a strong feeling of interventionof the control and, at the same time, to control behavior of a vehiclein such a manner as to also improve stability of the vehicle attitudeand riding comfort.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram depicting an entire configuration of a vehicleequipped with a vehicle behavior control device according to anembodiment of the present invention.

FIG. 2 is a block diagram depicting an electrical configuration of thevehicle behavior control device according to the embodiment of thepresent invention.

FIG. 3 is a flowchart of engine control processing to be performed bythe vehicle behavior control device according to the embodiment of thepresent invention, so as to control an engine.

FIG. 4 is a flowchart of torque reduction amount-deciding processing tobe performed by the vehicle behavior control device according to theembodiment of the present invention, so as to decide a torque reductionamount.

FIG. 5 is a map depicting a relationship between a steering speed, and atarget additional deceleration to be decided by the vehicle behaviorcontrol device according to the embodiment of the present invention.

FIG. 6 is a time chart depicting a temporal change of each parameterpertaining to engine control during turning of a vehicle equipped withthe vehicle behavior control device according to the embodiment of thepresent invention, wherein: the chart (a) is a plan view schematicallydepicting the vehicle which is turning in a clockwise direction; thechart (b) is a diagram depicting a change in steering wheel angle of thevehicle which is turning in the clockwise direction; the chart (c) is adiagram depicting a change in steering speed of the vehicle which isturning in the clockwise direction; the chart (d) is a diagram depictinga value of a torque reduction flag set based on the steering speed; thechart (e) is a diagram depicting a change in additional decelerationdecided based on the steering speed and the torque reduction flag; thechart (f) is a diagram depicting a change in torque reduction amountdecided based on the additional deceleration; and the chart (g) is adiagram depicting a change in final target torque decided based on abasic target torque and the torque reduction amount.

FIG. 7A is a diagram depicting a change in longitudinal acceleration andlateral acceleration during turning of the vehicle equipped with thevehicle behavior control device according to the embodiment of thepresent invention.

FIG. 7B is a diagram depicting the change in longitudinal accelerationand lateral acceleration during turning of the vehicle equipped with thevehicle behavior control device according to the embodiment of thepresent invention.

FIG. 8 is a diagram depicting measurement results of vehicle behaviorwhen the vehicle equipped with the vehicle behavior control deviceaccording to the embodiment of the present invention is caused toperform turning traveling, wherein: the chart (a) is a diagram depictinga change in steering wheel angle of the vehicle; the chart (b) is adiagram depicting a change in lateral jerk which is generated in thevehicle; the chart (c) is a diagram depicting a value of the torquereduction flag set based on the steering speed; the chart (d) is adiagram depicting a change in drive torque which drives a front roadwheel; and the chart (e) is a diagram depicting a change in longitudinaljerk which is generated in the vehicle.

FIG. 9 is a diagram depicting the manner of generation of the lateralacceleration and the longitudinal acceleration when each of the vehicleequipped with the vehicle behavior control device according to theembodiment of the present invention and a vehicle which is not equippedwith the vehicle behavior control device is caused to perform turningtraveling.

FIG. 10 is a diagram depicting the manner of occurrence of rolling andpitching when each of the vehicle equipped with the vehicle behaviorcontrol device according to the embodiment of the present invention andthe vehicle which is not equipped with the vehicle behavior controldevice is caused to perform turning traveling.

FIG. 11A is a schematic view depicting the vehicle attitude in terms ofan amount of expansion or contraction of a suspension of each roadwheel, and is also a view depicting the vehicle attitude when parallelrolling occurs.

FIG. 11B is a schematic view depicting the vehicle attitude in terms ofthe amount of expansion or contraction of the suspension of each roadwheel, and is also a view depicting the vehicle attitude when diagonalroll occurs.

FIG. 12A is a diagram depicting the manner of change in vertical load onthe front road wheel when each of the vehicle equipped with the vehiclebehavior control device according to the embodiment of the presentinvention and the vehicle which is not equipped with the vehiclebehavior control device is caused to perform turning traveling, and isalso a diagram depicting a change in vertical load on an inner frontroad wheel which is caused by a lateral load shift.

FIG. 12B is a diagram depicting the manner of change in vertical load onthe front road wheel when each of the vehicle equipped with the vehiclebehavior control device according to the embodiment of the presentinvention and the vehicle which is not equipped with the vehiclebehavior control device is caused to perform turning traveling, and isalso a diagram depicting a change in vertical load on the front roadwheels which is caused by a deceleration of the vehicle.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, a vehicle behavior controldevice according to an embodiment of the present invention will now bedescribed.

First of all, with reference to FIG. 1, a vehicle equipped with thevehicle behavior control device according to the embodiment of thepresent invention will be described. FIG. 1 is a block diagram depictingan entire configuration of the vehicle equipped with the vehiclebehavior control device according to the embodiment of the presentinvention.

In FIG. 1, the reference sign 1 denotes the vehicle equipped with thevehicle behavior control device according to this embodiment. A vehiclebody of the vehicle 1 has a front portion on which an engine 4 fordriving drive road wheels (in the example depicted in FIG. 1, right andleft front road wheels 2) is mounted. The engine 4 is an internalcombustion engine such as a gasoline engine or a diesel engine.

The vehicle 1 has: a steering wheel angle sensor 8 for detecting arotational angle of a steering wheel 6; an accelerator position sensor10 for detecting an amount of depression of an accelerator pedal(accelerator position); and a vehicle speed sensor 12 for detecting avehicle speed. Each of the above sensors is operable to output adetection value to a PCM (Power-train Control Module) 14.

Subsequently, with reference to FIG. 2, an electrical configuration ofthe vehicle behavior control device according to the embodiment of thepresent invention will be described. FIG. 2 is a block diagram depictingthe electrical configuration of the vehicle behavior control deviceaccording to the embodiment of the present invention.

The PCM 14 according to the embodiment of the present invention isconfigured to, based on detection signals output from various sensorsfor detecting an operating state of the engine 4 besides detectionsignals output from the above sensors 8 to 12, output control signals toperform controls with respect to respective constitutional elements(e.g., a throttle valve, a turbocharger, a variable valve mechanism, anignition unit, a fuel injection valve, and an EGR unit) of the engine 4.

The PCM 14 includes: a basic target torque-deciding part 16 for decidinga basic target torque based on a driving state of the vehicle 1including an accelerator pedal operation; a torque reductionamount-deciding part 18 for deciding a torque reduction amount foradding a deceleration to the vehicle 1 based on a quantity relating to ajerk in the vehicle width direction of the vehicle 1 (lateraljerk-related quantity); a final target torque-deciding part 20 fordeciding a final target torque based on the basic target torque and thetorque reduction amount; and an engine control part 22 for controllingthe engine 4 to cause the engine 4 to output the final target torque.This embodiment will be described based on an example where the torquereduction amount-deciding part 18 uses a steering speed of the vehicle 1as the lateral jerk-related quantity.

Respective components of the PCM 14 are functionally realized by acomputer which includes: a CPU; various programs (including a basiccontrol program such as an OS, and an application program capable ofbeing activated on the OS to realize a specific function) to beinterpreted and executed on the CPU; and an internal memory such as aROM or a RAM for storing the programs and various data.

A PCM 14 is equivalent to “vehicle behavior control device” according tothe present invention, and functions as “steering speed acquiring part”and “vertical load increasing part”, although details thereof will bedescribed later.

Subsequently, with reference to FIGS. 3 to 5, processing to be performedby the vehicle behavior control device will be described.

FIG. 3 is a flowchart of engine control processing to be performed bythe vehicle behavior control device according to the embodiment of thepresent invention, so as to control the engine 4. FIG. 4 is a flowchartof torque reduction amount-deciding processing to be performed by thevehicle behavior control device according to the embodiment of thepresent invention, so as to decide the torque reduction amount. FIG. 5is a map depicting a relationship between the steering speed, and atarget additional deceleration to be decided by the vehicle behaviorcontrol device according to the embodiment of the present invention.

The engine control processing in FIG. 3 is activated when an ignitionswitch of the vehicle 1 is turned on to apply power to the vehiclebehavior control device, and repeatedly executed.

As depicted in FIG. 3, upon start of the engine control processing, instep S1, the PCM 14 operates to acquire various information about thedriving state of the vehicle 1. Specifically, the PCM 14 operates toacquire, as information about the driving state, detection signalsoutput from the aforementioned various sensors, including the steeringwheel angle detected by the steering wheel angle sensor 8, theaccelerator position detected by the accelerator position sensor 10, thevehicle speed detected by the vehicle speed sensor 12, and a gear stagecurrently set in a transmission of the vehicle 1.

Subsequently, in step S2, the basic target torque-deciding part 16 ofthe PCM 14 operates to set a target acceleration based on the drivingstate of the vehicle 1 including the accelerator pedal operation,acquired in step S1. Specifically, the basic target torque-deciding part16 operates to select, from acceleration characteristic maps in whichvarious vehicle speeds and various gear stages are defined (the maps arepreliminarily created and stored in a memory or the like), anacceleration characteristic map which corresponds to a current vehiclespeed and a current gear stage, and decide a target accelerationcorresponding to a current accelerator position, with reference to theselected acceleration characteristic map.

Subsequently, in step S3, the basic target torque-deciding part 16operates to decide the basic target torque of the engine 4 for realizingthe target acceleration decided in step S2. In this embodiment, thebasic target torque-deciding part 16 operates to decide the basic targettorque within a torque range outputtable by the engine 4, based oncurrent vehicle speed, gear stage, road grade, road surface μ, etc.

In parallel to the processing in steps S2 and S3, in step S4, the torquereduction amount-deciding part 18 operates to perform the torquereduction amount-deciding processing of deciding the torque reductionamount for adding a deceleration to the vehicle 1, based on a steeringwheel operation. This torque reduction amount-deciding processing willbe described with reference to FIG. 4.

As depicted in FIG. 4, upon start of the torque reductionamount-deciding processing, in step S21, the torque reductionamount-deciding part 18 operates to calculate the steering speed basedon the steering wheel angle acquired in step S1.

Subsequently, in step S22, the torque reduction amount-deciding part 18operates to determine whether or not the steering speed is greater thana given threshold T_(S1).

As a result, when the steering speed is greater than the thresholdT_(S1), the processing advances to step S23. In step S23, the torquereduction amount-deciding part 18 operates to set the torque reductionflag, indicative of whether or not a condition for allowing reduction ofan output torque of the engine 4 so as to add a deceleration to thevehicle 1 is satisfied, to True (true value) indicative of a state inwhich the condition for allowing the torque reduction is satisfied.

Subsequently, in step S24, the torque reduction amount-deciding part 18operates to acquire the target additional deceleration based on thesteering speed. This target additional deceleration is a deceleration tobe added to the vehicle 1 according to the steering wheel operation inorder to accurately realize vehicle behavior which is intended by adriver.

Specifically, the torque reduction amount-deciding part 18 operates toacquire a target additional deceleration which corresponds to thesteering speed calculated in step S21, based on a relationship betweenthe target additional deceleration and the steering speed, representedby the map in FIG. 5.

In FIG. 5, the horizontal axis represents the steering speed, and thevertical axis represents the target additional deceleration. As depictedin FIG. 5, when the steering speed is equal to or less than a thresholdT_(S), a corresponding target additional deceleration is 0. That is,when the steering speed is equal to or less than the threshold T_(S1),the PCM 14 operates to stop control of adding a deceleration to thevehicle 1 (specifically, reduction of an output torque of the engine 4)based on the steering wheel operation.

On the other hand, when the steering speed is greater than the thresholdT_(S1), as the steering speed is increased to a higher value, a targetadditional deceleration which corresponds to the steering speed comescloser to a given upper limit value D_(max). That is, as the steeringspeed is increased to a higher value, the target additional decelerationis increased, and a rate of increase of the target additionaldeceleration becomes smaller. This upper limit value D_(max) is set to adeceleration (e.g., 0.5 m/s²≅0.05 G) to the extent that a driver doesnot feel intervention of the control even when the deceleration is addedto the vehicle 1 according to the steering wheel operation.

Further, when the steering speed is equal to or greater than a thresholdT_(S2) which is greater than the threshold T_(S1), the target additionaldeceleration is maintained at the upper limit value D_(max).

Subsequently, in step S25, the torque reduction amount-deciding part 18operates to decide an additional deceleration in the current processing,under a condition that a change rate of the additional deceleration isequal to or less than a threshold Rmax (e.g., 0.5 m/s³).

Specifically, the torque reduction amount-deciding part 18 operates to,when a change rate from the additional deceleration decided in the lastprocessing to the target additional deceleration acquired in step S24 inthe current processing is equal to or less than the threshold Rmax,decide the target additional deceleration acquired in step S24, as theadditional deceleration in the current processing.

On the other hand, the torque reduction amount-deciding part 18 operatesto, when the change rate from the additional deceleration decided in thelast processing to the target additional deceleration acquired in stepS24 in the current processing is greater than the threshold Rmax,decide, as the additional deceleration in the current processing, avalue obtained by changing the additional deceleration decided in thelast processing until the current processing at the change rate Rmax.

Subsequently, in step S26, the torque reduction amount-deciding part 18operates to decide the torque reduction amount, based on the currentadditional deceleration decided in step S25. Specifically, the torquereduction amount-deciding part 18 operates to decide a torque reductionamount required for realizing the current additional deceleration, basedon the current vehicle speed, gear stage, road gradient and othersacquired in step S1.

On the other hand, in step S22, when the steering speed is not greaterthan the threshold T_(S1), (i.e., when the steering speed is equal to orlower than the threshold T_(S1)), the processing advances to step S27.In step S27, the torque reduction amount-deciding part 18 operates toset the torque reduction flag, indicative of whether or not thecondition for allowing reduction of the output torque of the engine 4 soas to add a deceleration to the vehicle 1 is satisfied, to False (falsevalue) indicative of a state in which the condition for allowing thetorque reduction is not satisfied.

After completion of step S26 or S27, the torque reductionamount-deciding part 18 operates to finish the torque reductionamount-deciding processing, and the processing returns to the mainroutine.

Returning to FIG. 3, after performing the processing in steps S2 and S3and the torque reduction amount-deciding processing in step S4, in stepS5, the final target torque-deciding part 20 operates to subtract thetorque reduction amount decided in the torque reduction amount-decidingprocessing in step S4, from the basic target torque decided in step S3,to thereby decide the final target torque.

Subsequently, in step S6, the engine control part 22 operates to controlthe engine 4 to cause the engine 4 to output the final target torque setin step S5. Specifically, the engine control part 22 operates to, basedon the final target torque set in step S5 and an engine speed, decidevarious state amounts (e.g., air charge amount, fuel injection amount,intake-air temperature, and oxygen concentration) required for realizingthe final target torque, and then, based on the decided state amounts,control respective actuators for driving the respective constitutionalelements of the engine 4. In this case, the engine control part 22operates to set a limit value or a limit range corresponding to thestate amount, and set a controlled variable of each actuator to enableits related state amount to preserve limitation by the limit value orthe limit range, so as to execute control.

After completion of step S6, the PCM 14 operates to finish the enginecontrol processing.

Next, with reference to FIG. 6, an example of an engine control by thevehicle behavior control device according to the embodiment of thepresent invention will be described. FIG. 6 is a time chart depicting atemporal change of parameters pertaining to the engine control duringturning of the vehicle 1 equipped with the vehicle behavior controldevice according to the embodiment of the present invention.

The chart (a) of FIG. 6 is a plan view schematically depicting thevehicle 1 which is turning in a clockwise direction. As depicted in thechart (a) of FIG. 6, the vehicle 1 starts turning in the clockwisedirection from a position A, and continues turning in the clockwisedirection at a constant steering wheel angle from a position B to aposition C.

The chart (b) of FIG. 6 is a diagram depicting a change in steeringwheel angle of the vehicle 1 which is turning in the clockwise directionas depicted in the chart (a) of FIG. 6. In the chart (b) of FIG. 6, thehorizontal axis represents the time, and the vertical axis representsthe steering wheel angle.

As depicted in the chart (b) of FIG. 6, clockwise steering is started atthe position A, and then, along with an additional turning operation ofthe steering wheel, a clockwise steering wheel angle graduallyincreases, and the clockwise steering wheel angle reaches maximum at theposition B. Thereafter, the steering wheel angle is maintained constantuntil the position C (maintaining of steering wheel).

The chart (c) of FIG. 6 is a diagram depicting a change in steeringspeed of the vehicle 1 which is turning in the clockwise direction asdepicted in the chart (a) of FIG. 6. In the chart (c) of FIG. 6, thehorizontal axis represents the time, and the vertical axis representsthe steering speed.

The steering speed of the vehicle 1 is expressed as a temporaldifferentiation of the steering wheel angle of the vehicle 1. That is,as depicted in the chart (c) of FIG. 6, when clockwise steering isstarted at the position A, a clockwise steering speed arises, and thesteering speed is maintained approximately constant in an intermediatezone between the position A and the position B. Thereafter, theclockwise steering speed decreases and, when the clockwise steeringwheel angle reaches maximum at the position B, the steering speedbecomes 0. Further, in an intermediate zone between the position B andthe position C where the clockwise steering wheel angle is maintained,the steering speed remains at 0.

The chart (d) of FIG. 6 is a diagram depicting a truth value of thetorque reduction flag set based on the steering speed. In the chart (d)of FIG. 6, the horizontal axis represents the time, and the verticalaxis represents the truth value of the torque reduction flag.

As depicted in the chart (d) of FIG. 6, before clockwise steering isstarted at the position A, the torque reduction flag is set to False.After the clockwise steering is started at the position A, the torquereduction flag is changed from False to True when the steering speedexceeds the threshold T_(S1). Thereafter, the steering speed decreasesas the vehicle 1 approaches the position B and, when the steering speedbecomes equal to or lower than the threshold T_(S1), the torquereduction flag is changed from True to False.

The chart (e) of FIG. 6 is a diagram depicting a change in additionaldeceleration decided based on the steering speed and the torquereduction flag. In the chart (e) of FIG. 6, the horizontal axisrepresents the time, and the vertical axis represents the additionaldeceleration.

As described with reference to FIG. 4, the torque reductionamount-deciding part 18 operates, when the steering speed is greaterthan the threshold T_(S1) (that is, when the torque reduction flag isTrue) in step S22, to acquire the target additional deceleration basedon the steering speed in step S24. Subsequently, in step S25, the torquereduction amount-deciding part 18 operates to decide the additionaldeceleration in each processing cycle, under a condition that theincrease rate of the additional deceleration is equal to or less thanthe threshold Rmax.

As depicted in the chart (e) of FIG. 6, the additional decelerationstarts increasing from a point at which the torque reduction flag isswitched from False to True, and is maintained approximately constant inan intermediate zone between the position A and the position B.Thereafter, the additional deceleration decreases in accordance with adecrease in steering speed, and becomes 0 when the torque reduction flagis switched from True to False.

The chart (f) of FIG. 6 is a diagram depicting a change in torquereduction amount decided based on the additional deceleration depictedin the chart (e) of FIG. 6. In the chart (f) of FIG. 6, the horizontalaxis represents the time, and the vertical axis represents the torquereduction amount.

As mentioned above, the torque reduction amount-deciding part 18operates to decide the torque reduction amount required for realizing anadditional deceleration, based on parameters such as the current vehiclespeed, gear stage and road grade. Thus, in the case where theseparameters are constant, the torque reduction amount is decided so as tochange in the same pattern as that of the additional decelerationdepicted in the chart (e) of FIG. 6.

The chart (g) of FIG. 6 is a diagram depicting a change in final targettorque decided based on the basic target torque and the torque reductionamount. In the chart (g) of FIG. 6, the horizontal axis represents thetime, and the vertical axis represents the torque. Further, in the chart(g) of FIG. 6, the broken line indicates the basic target torque, andthe solid line indicates the final target torque.

As described with reference to FIG. 3, the final target torque-decidingpart 20 operates to subtract the torque reduction amount decided in thetorque reduction amount-deciding processing in step S4, from the basictarget torque decided in step S3, to thereby decide the final targettorque.

That is, as depicted in the chart (g) of FIG. 6, during a period wherethe torque reduction flag is set to True in an intermediate zone betweenthe position A and the position B, the final target torque is reducedfrom the basic target torque by an amount corresponding to the torquereduction amount, and deceleration which corresponds to this torquereduction is generated in the vehicle 1 and hence, a load shift to thefront road wheels 2 occurs. As a result, a frictional force between thefront road wheels 2 and a road surface increases so that a corneringforce of the front road wheels 2 increases.

Subsequently, a change in longitudinal acceleration and lateralacceleration generated in a vehicle due to a control performed by thevehicle behavior control device according to the embodiment of thepresent invention will be described with reference to FIGS. 7A and 7B.FIG. 7A is a diagram depicting a change in longitudinal acceleration andlateral acceleration during a period from at a time when the vehicleequipped with the vehicle behavior control device according to theembodiment of the present invention starts to perform turning in theclockwise direction from straight traveling as depicted in chart (a) ofFIG. 6 until the vehicle starts to perform regular circle turning, andFIG. 7B is a diagram depicting an extremely-small-acceleration region(that is, an initial stage of turning) in FIG. 7A in an enlarged manner.In FIGS. 7A and 7B, the horizontal axis represents the lateralacceleration (the acceleration to the right side in the vehicle widthdirection has a positive value), and the vertical axis represents thelongitudinal acceleration (acceleration in a traveling direction has apositive value, and deceleration in the traveling direction has anegative value).

Further, in FIGS. 7A and 7B, the solid line indicates a change inlongitudinal acceleration and lateral acceleration of the vehicleequipped with the vehicle behavior control device according to theembodiment of the present invention. The one-dot chain line indicates achange in longitudinal acceleration and lateral acceleration of thevehicle equipped with a conventional vehicle motion control device asdescribed in Patent Literature 1. The broken line indicates a change inlongitudinal acceleration and lateral acceleration when control is notperformed by these control devices.

As indicated by the one-dot chain line in FIG. 7A, in the conventionalvehicle motion control device as described in Patent Literature 1, onlya steering operation for turning performed by a driver causes adeceleration to increase or decrease in accordance with an increase inlateral acceleration such that an acceleration obtained by synthesizinga lateral acceleration and a longitudinal acceleration traces an arcshape in a counterclockwise direction. That is, to realize a vehiclemotion like a motion performed by an expert driver where a syntheticacceleration traces an arc shape in the counterclockwise direction at aconstant rate, the control device causes a deceleration substantiallyequal to a lateral acceleration, which is generated in the vehicle inaccordance with steering operation performed by the driver, to generateand, thereafter, causes the deceleration to decrease. To allow a driverto feel that the synthetic acceleration is varying at a constant rate, amagnitude of deceleration which is generated by the control may reach0.5 G. A deceleration of 0.5 G is deceleration which is generated by astrong braking operation performed in case of emergency, and at which apassenger standing on a bus may fall, for example. Accordingly, a driverwho does not perform a deceleration operation may experience a strongfeeling of intervention of the control.

On the other hand, as indicated by the solid line in FIG. 7A, adeceleration to be generated by the control performed by the vehiclebehavior control device according to the embodiment of the presentinvention is limited to approximately 0.001 G to 0.01 G, and to 0.05 G(upper limit value D_(max) of the target additional deceleration) atmaximum. A deceleration of 0.05 G is substantially equal to adeceleration which is indicated by the broken line in FIG. 7A, and isgenerated during turning when control by the control devices is notperformed (that is, a deceleration caused by a drag force which isgenerated by a frictional force between a road surface and a roadwheel). Accordingly, the driver does not notice that a control of addinga deceleration is being performed.

Particularly, as depicted in FIG. 7B in an enlarged manner, the PCM 14in this embodiment starts to reduce an output torque of the engine 4when the steering speed becomes equal to or greater than the thresholdT_(S1) at the initial stage of turning of the vehicle thus causing thetorque reduction flag to be set to True, and the PCM 14 causes adeceleration to rapidly increase in a region where the lateralacceleration is extremely small. With such a configuration, adeceleration rises more promptly compared to the case where control ofadding a deceleration is not performed. Accordingly, when a driverstarts a steering wheel operation, a vertical load on the front roadwheels can be immediately increased so as to increase a cornering forceand hence, it is possible to improve responsivity of vehicle behaviorand a linear feeling with respect to the steering wheel operation.

Subsequently, vehicle behavior when the vehicle equipped with thevehicle behavior control device according to the embodiment of thepresent invention is caused to perform turning traveling will bedescribed with reference to FIG. 8 to FIG. 12.

To evaluate the manner of change in vehicle behavior when an outputtorque of the engine 4 is reduced in accordance with a lateral jerkwhich is generated with steering input at the initial stage of turning,inventors of the present invention caused the vehicle equipped with thevehicle behavior control device according to the above embodiment totravel a single corner where the vehicle transitions from straighttraveling to regular circle turning at a constant vehicle speed. Theinventors measured various parameters pertaining to vehicle behaviorover this period.

FIG. 8 is a diagram depicting measurement results of vehicle behaviorwhen the vehicle equipped with the vehicle behavior control deviceaccording to this embodiment is caused to perform turning traveling,wherein: the chart (a) of FIG. 8 is a diagram depicting a change insteering wheel angle of the vehicle; the chart (b) of FIG. 8 is adiagram depicting a change in lateral jerk which is generated in thevehicle; the chart (c) of FIG. 8 is a diagram depicting a value of thetorque reduction flag set based on the steering speed; the chart (d) ofFIG. 8 is a diagram depicting a change in drive torque which drives afront road wheel; and the chart (e) of FIG. 8 is a diagram depicting achange in longitudinal jerk which is generated on the vehicle. In thechart (d) of FIG. 8 and the chart (e) of FIG. 8, the solid lineindicates the result of the vehicle equipped with the vehicle behaviorcontrol device of this embodiment, and the broken line indicates theresult of the conventional vehicle which is not equipped with thevehicle behavior control device.

An increase in slip angle of the front road wheels along with anincrease in steering wheel angle generates a cornering force due to africtional force between a road surface and a ground contact surface ofthe front road wheels. Due to such generation of cornering force, alateral jerk is generated substantially simultaneously with the start ofan increase in steering wheel angle as depicted in charts (a) and (b) ofFIG. 8. The lateral jerk changes substantially in the same pattern asthe steering speed obtained by time-differentiating a steering wheelangle.

As depicted in the chart (c) of FIG. 8, the torque reduction flag is setto True during the period that a lateral jerk is generated, that is,during the period that the steering speed is generated, so that a drivetorque is reduced as indicated by the solid line in the chart (d) ofFIG. 8. As described above, it can be seen that the vehicle behaviorcontrol device is operated as described with reference to FIG. 6.

When a slip angle of the front road wheels 2 is increased, a drag forceis also generated due to a frictional force between the road surface andthe ground contact surface of the front road wheels. Due to a complianceelement of a suspension or the like, a slight delay is present betweenthe generation of the drag force and the generation of deceleration inthe vehicle due to such a drag force. Accordingly, in the vehicle whichis not equipped with the vehicle behavior control device of thisembodiment, as indicated by the broken line in the chart (e) of FIG. 8,a rearward jerk (deceleration jerk) in the longitudinal direction of thevehicle is generated at a later time than a lateral jerk.

On the other hand, in the vehicle equipped with the vehicle behaviorcontrol device of this embodiment, drive torque reduction is startedimmediately after a steering speed becomes equal to or greater than thethreshold T_(S1) so that the torque reduction flag is set to True.Accordingly, as indicated by the solid line in the chart (e) of FIG. 8,at a timing earlier than a deceleration jerk caused only by a dragforce, a deceleration jerk is generated substantially simultaneouslywith the generation of a lateral jerk thus allowing a peak of thedeceleration jerk to appear at a time earlier than a peak of the lateraljerk. Accordingly, immediately after the lateral jerk is generated, avertical load on the front road wheels is increased and hence, it ispossible to control behavior of the vehicle with good responsivity withrespect to a steering wheel operation performed by a driver.

FIG. 9 is a diagram depicting the manner of generation of the lateralacceleration and the longitudinal acceleration during theabove-mentioned turning traveling. In FIG. 9, the horizontal axisrepresents the acceleration in a vehicle width direction (lateralacceleration), and the vertical axis represents the acceleration in alongitudinal direction (longitudinal acceleration). Further, in FIG. 9,acceleration in a deceleration direction (deceleration) is expressed asa negative value.

As mentioned above, in the vehicle which is not equipped with thevehicle behavior control device of this embodiment, when a steeringwheel angle starts to increase, a deceleration jerk is generated at alater time than a lateral jerk. Accordingly, as indicated by the brokenline in FIG. 9, a deceleration does not increase on the rise of alateral acceleration (0 to 0.1 G) and, when the lateral accelerationincreases (that is, when a cornering force increases), the decelerationincreases in accordance with an increase in drag force.

On the other hand, in the vehicle equipped with the vehicle behaviorcontrol device of this embodiment, a reduction of driving force of thevehicle is started when the steering speed becomes equal to or greaterthan the threshold T_(S1). Accordingly, at a timing earlier than adeceleration jerk caused only by a drag force, a deceleration jerk isgenerated substantially simultaneously with the generation of a lateraljerk thus allowing the peak of the deceleration jerk to appear at a timeearlier than the peak of the lateral jerk. Therefore, as indicated bythe solid line in FIG. 9, a deceleration also rises following the riseof a lateral acceleration (0 to 0.1 G) so that the lateral accelerationand the deceleration vary while maintaining a linear relationship.Accordingly, it is possible to not only control behavior of the vehiclewith good responsivity with respect to a steering wheel operationperformed by a driver but also control behavior of the vehicle in such amanner as to also improve stability of the vehicle attitude and ridingcomfort.

FIG. 10 is a diagram depicting the manner of occurrence of rolling andpitching during the above-mentioned turning traveling. In FIG. 10, thehorizontal axis represents a roll angle, and the vertical axisrepresents a pitch angle. Further, in FIG. 10, a pitch angle in adirection that a front portion of the vehicle dips is expressed as anegative value.

As mentioned above, in the vehicle which is not equipped with thevehicle behavior control device of this embodiment, when a steeringwheel angle starts to increase, a deceleration jerk is generated at alater time than a lateral jerk so that a deceleration does not increaseon the rise of a lateral acceleration. Accordingly, as indicated by thebroken line in FIG. 10, a load shift occurs in the vehicle widthdirection of the vehicle in accordance with an increase in lateralacceleration thus increasing a roll angle. However, a pitch angleincreases or decreases irrespective of an increase in roll angle.

On the other hand, in the vehicle equipped with the vehicle behaviorcontrol device of this embodiment, a reduction of driving force of thevehicle is started when the steering speed becomes equal to or greaterthan the threshold T_(S1). Accordingly, a deceleration jerk is generatedsubstantially simultaneously with the generation of a lateral jerk sothat a deceleration is also caused to rise following the rise of alateral acceleration. Therefore, a pitch angle is increased in thedirection that the front portion of the vehicle dips in synchronizationwith an increase in roll angle.

FIGS. 11A and 11B are schematic views depicting the vehicle attitude interms of an amount of expansion or contraction of a suspension of eachroad wheel, wherein: FIG. 11A is a view depicting the vehicle attitudewhen parallel rolling occurs, and FIG. 11B is a view depicting thevehicle attitude when diagonal roll occurs.

As mentioned above, in the vehicle which is not equipped with thevehicle behavior control device of this embodiment, a load shift occursin the vehicle width direction of the vehicle in accordance with anincrease in lateral acceleration thus increasing a roll angle. However,a pitch angle increases or decreases irrespective of an increase in rollangle. Accordingly, at the initial stage of turning, only a roll angleincreases so that the parallel roll attitude as depicted in FIG. 11A isassumed and, thereafter, the forward inclined attitude or the rearwardinclined attitude is assumed due to pitching which occurs irrespectiveof a roll angle.

On the other hand, in the vehicle equipped with the vehicle behaviorcontrol device of this embodiment, a reduction of driving force of thevehicle is started when the steering speed becomes equal to or greaterthan the threshold T_(S1) so that a pitch angle is increased in adirection that the front portion of the vehicle dips in synchronizationwith an increase in roll angle. Accordingly, at the initial stage ofturning, rolling and pitching in which the front portion of the vehicledips occur in synchronization with each other and hence, the diagonalroll attitude as depicted in FIG. 11B is assumed.

As described above, in the vehicle behavior control device according tothe present invention, a driving force reduction amount is promptlyincreased in a region at the initial stage of turning where the lateralacceleration is extremely small so that a situation in which the vehicleattitude may smoothly shift to a diagonal roll attitude is created whena driver starts a steering wheel operation. Such a configuration causesthe cornering force of the front road wheels to increase thus improvingresponsivity of turning behavior and, at the same time, allows a driverto precisely recognize the generation and continuation of the turningbehavior from that point.

FIGS. 12A and 12B are diagrams depicting the manner of change invertical load on the front road wheels during the above-mentionedturning traveling, wherein: FIG. 12A is a diagram depicting a change invertical load on the inner front road wheel which is caused by a lateralload shift; and FIG. 12B is a diagram depicting a change in verticalload on the front road wheels which is caused by a deceleration of thevehicle.

As mentioned above, in the vehicle which is not equipped with thevehicle behavior control device of this embodiment, when steering wheelangle starts to increase, a deceleration does not increase on the riseof a lateral acceleration and hence, as indicated by the broken line inFIGS. 12A and 12B, an amount of lateral load shift of the front roadwheels linearly increases in accordance with an increase in lateralacceleration. However, at the rise (0 to 0.1 G) of the lateralacceleration, a longitudinal load shift is not generated by thedeceleration and hence, a change in vertical load on the front roadwheels does not occur due to the deceleration. Therefore, when lateralacceleration increases, deceleration increases in accordance with anincrease in drag force, thus increasing an amount of change in verticalload on the front road wheels which is caused by the deceleration.

On the other hand, in the vehicle equipped with the vehicle behaviorcontrol device of this embodiment, a reduction of driving force of thevehicle is started when the steering speed becomes equal to or greaterthan the threshold T_(S1). Accordingly, deceleration also risesfollowing the rise of the lateral acceleration so that the lateralacceleration and the deceleration vary while maintaining a linearrelationship. Therefore, as indicated by the solid line in FIGS. 12A and12B, in synchronization with a linear increase in amount of lateral loadshift of the front road wheels in accordance with an increase in lateralacceleration, a longitudinal load shift is generated by decelerationthus increasing an amount of change in vertical load on the front roadwheels from the rise (0 to 0.1 G) of the lateral acceleration. With sucha configuration, at the initial stage of turning of the vehicle, avertical load on the front road wheels is increased so as to suppress adecrease in vertical load on the inner front road wheel which is causedby lateral load shift thus increasing a cornering force of the frontroad wheels and hence, responsivity of turning behavior can be improved.

Subsequently, another modification of the embodiment of the presentinvention will be described.

The above embodiment has been described based on an example where atorque reduction amount-deciding part 18 operates to acquire the targetadditional deceleration based on the steering speed, and decide thetorque reduction amount based on the target additional deceleration.However, the torque reduction amount-deciding part 18 may operate todecide the torque reduction amount based on any driving state of thevehicle 1 other than the accelerator pedal operation (e.g., steeringwheel angle, lateral acceleration, yaw rate, slip ratio or the like).

For example, the torque reduction amount-deciding part 18 may operate toacquire a target additional deceleration based on a lateral accelerationinput from an acceleration sensor or a lateral jerk obtained bytime-differentiating a lateral acceleration, and decide a torquereduction amount.

The above embodiment has been described based on an example where thePCM 14 reduces an output torque of the engine 4 in accordance with thetarget additional deceleration thus generating a rearward decelerationjerk in the longitudinal direction in the vehicle 1 so that a pitchangle is increased in a direction that the front portion of the vehicledips and, at the same time, a vertical load on the front road wheels isincreased. However, the configuration may be adopted where adeceleration jerk is generated by an active engine mount which supportsthe engine 4 in a vertically movable manner or by an active suspensionwhich can control operation and characteristics of the suspension, and apitch angle is increased in a direction that the front portion of thevehicle dips and, at the same time, a vertical load on the front roadwheels is increased.

The above embodiment has been described based on an example where thevehicle 1 equipped with the vehicle behavior control device mounts theengine 4 for driving drive road wheels. However, the vehicle behaviorcontrol device of the present invention is also applicable to a vehiclewhich mounts a motor for driving drive road wheels by electricitysupplied from a battery or capacitor. In this case, a PCM 14 isconfigured to perform control of reducing a torque of the motoraccording to a steering speed of the vehicle 1.

Subsequently, advantageous effects of the vehicle behavior controldevices of the above embodiment of the present invention and themodification of the embodiment of the present invention will bedescribed.

First of all, the PCM 14 starts to reduce an output torque of the engine4 based on a lateral jerk-related quantity when the torque reductionflag is set to True, indicative of a state in which the condition forallowing reduction of an output torque of the engine 4 is satisfied.Accordingly, immediately after a lateral jerk is generated in thevehicle 1, the output torque of the engine 4 is reduced so as toincrease a vertical load on the front road wheels and hence, it ispossible to control behavior of the vehicle 1 with good responsivitywith respect to a steering wheel operation performed by driver.Therefore, it is possible to improve responsivity of vehicle behaviorand a linear feeling with respect to the steering wheel operationwithout causing the driver to experience a strong feeling ofintervention of the control. Further, behavior which is intended by thedriver is accurately realized and hence, extremely small correctionsteering becomes unnecessary thus also improving stability of thevehicle attitude and riding comfort.

Further, the PCM 14 sets, when a lateral jerk-related quantity exceeds agiven threshold, the torque reduction flag to True. Accordingly, whenthe lateral jerk-related quantity is equal to or lower than thethreshold, it is possible to suppress the excessive reaction of thevehicle 1 with respect to an extremely small steering wheel operation.Therefore, it is possible to control behavior of a vehicle in such amanner as to accurately realize a behavior which is intended by thedriver without causing the driver to feel discomfort with respect tovehicle behavior during straight traveling.

The lateral jerk-related quantity is a steering speed of the vehicle 1and hence, a driving force can be immediately reduced in response to thestart of a steering wheel operation performed by a driver. Therefore, itis possible to control behavior of the vehicle 1 with betterresponsivity with respect to the steering wheel operation performed bythe driver.

The PCM 14 generates, when the steering speed becomes equal to orgreater than the threshold T_(S1), a rearward deceleration jerk in thelongitudinal direction of the vehicle 1 is generated and hence, afterthe driver starts the steering wheel operation, at a timing earlier thana deceleration jerk caused only by a drag force, a deceleration jerk canbe generated substantially simultaneously with the generation of alateral jerk. With such a configuration, at the initial stage of turningof the vehicle 1, the deceleration jerk is immediately generatedaccording to the steering wheel operation so as to increase adeceleration thus increasing a vertical load on the front road wheels 2.Accordingly, it is possible to control behavior of the vehicle 1 withgood responsivity and a linear feeling with respect to the steeringwheel operation performed by the driver and, at the same time, tocontrol behavior of the vehicle 1 such that the deceleration also risesfollowing the rise of a lateral acceleration at the initial stage ofturning so that the lateral acceleration and the deceleration vary whilemaintaining a linear relationship. Therefore, behavior of the vehicle 1can be controlled in such a manner as to also improve stability of thevehicle attitude and riding comfort.

The PCM 14 starts, when the steering speed becomes equal to or greaterthan the threshold T_(S1), to reduce an output torque of the engine 4thus generating the deceleration jerk and hence, after the driver startsthe steering wheel operation, the deceleration jerk can be generatedwith high responsivity. Accordingly, it is possible to control behaviorof the vehicle 1 with better responsivity with respect to the steeringwheel operation performed by the driver and, at the same time, tocontrol behavior of the vehicle 1 in such a manner as to also furtherimprove stability of the vehicle attitude and riding comfort.

The PCM 14 generates, when the steering speed becomes equal to orgreater than the threshold T_(S1), a deceleration jerk such that thepeak of the deceleration jerk appears at a time earlier than the peak ofa lateral jerk and hence, at the initial stage of turning of the vehicle1, the deceleration jerk is immediately generated according to thesteering wheel operation so as to increase a deceleration thusincreasing a vertical load on the front road wheels 2. Accordingly, itis possible to control behavior of the vehicle 1 with betterresponsivity with respect to the steering wheel operation performed by adriver and, at the same time, to control behavior of the vehicle 1 insuch a manner as to also improve stability of the vehicle attitude andriding comfort.

The PCM 14 increases, when the steering speed becomes equal to orgreater than the threshold T_(S1), a pitch angle in a direction that thefront portion of the vehicle 1 dips and hence, after the driver startsthe steering wheel operation, pitching in which the front portion of thevehicle 1 dips can be caused to occur when rolling occurs. With such aconfiguration, at the initial stage of turning of the vehicle 1, thediagonal roll attitude is assumed so that a cornering force of the frontroad wheels 2 is increased thus improving responsivity of turningbehavior and, at the same time, allowing a driver to precisely recognizethe generation and continuation of the turning behavior from that point.Accordingly, it is possible to control behavior of the vehicle 1 withgood responsivity and a linear feeling with respect to the steeringwheel operation performed by the driver and, at the same time, tocontrol behavior of the vehicle 1 in such a manner as to also improvestability of the vehicle attitude and riding comfort.

The PCM 14 starts, when the steering speed becomes equal to or greaterthan the threshold T_(S1), to reduce an output torque of the engine 4thus increasing a pitch angle in a direction that the front portion ofthe vehicle 1 dips. Accordingly, after the driver starts the steeringwheel operation, a deceleration is generated in the vehicle 1 byreducing a driving force, so that a pitch angle can be increased withhigh responsivity. Therefore, it is possible to control behavior of thevehicle 1 with better responsivity with respect to the steering wheeloperation performed by the driver and, at the same time, to controlbehavior of the vehicle 1 in such a manner as to also further improvestability of the vehicle attitude and riding comfort.

The PCM 14 increases, when the steering speed becomes equal to orgreater than the threshold T_(S1), a pitch angle in a direction that thefront portion of the vehicle 1 dips in synchronization with an increasein roll angle of the vehicle 1 and hence, the diagonal roll attitude canbe reliably assumed at the initial stage of turning of the vehicle 1.Accordingly, it is possible to control behavior of the vehicle 1 withgood responsivity with respect to the steering wheel operation performedby the driver and, at the same time, to control behavior of the vehicle1 in such a manner as to also improve stability of the vehicle attitudeand riding comfort.

The PCM 14 increases, when the steering speed becomes equal to orgreater than the threshold T_(S1), a vertical load on the front roadwheels 2 and hence, after the driver starts the steering wheeloperation, the vertical load on the front road wheels 2 can be increasedwhen an amount of lateral load shift of the front road wheels 2 isincreased in accordance with an increase in lateral acceleration. Withsuch a configuration, at the initial stage of turning of the vehicle 1,the vertical load on the front road wheels 2 is increased so as tosuppress a decrease in vertical load on the inner front road wheel whichis caused by a lateral load shift so that a cornering force of the frontroad wheels 2 is increased thus improving responsivity of turningbehavior. Therefore, it is possible to improve responsivity of vehiclebehavior and a linear feeling with respect to the steering wheeloperation without causing the driver to experience a strong feeling ofintervention of the control. Further, behavior which is intended by thedriver is accurately realized and hence, extremely small correctionsteering becomes unnecessary thus also improving stability of thevehicle attitude and riding comfort.

The PCM 14 starts, when the steering speed becomes equal to or greaterthan the threshold T_(S1), to reduce a driving force of the vehicle 1thus increasing a vertical load on the front road wheels 2. Accordingly,after the driver starts the steering wheel operation, a deceleration isgenerated in the vehicle 1 by reducing a driving force, so that avertical load on the front road wheels 2 can be increased with highresponsivity. With such a configuration, at the initial stage ofturning, the vertical load on the front road wheels 2 is promptlyincreased so as to suppress a decrease in vertical load on the innerfront road wheel which is caused by lateral load shift so that acornering force of the front road wheels is increased thus improvingresponsivity of turning behavior.

The PCM 14 causes, when the steering speed becomes equal to or greaterthan the threshold T_(S1), a vertical load on the front road wheels 2 toincrease in synchronization with a lateral load shift of the front roadwheels 2. Accordingly, at the initial stage of turning of the vehicle 1,a vertical load on the front road wheels 2 can be increased such that adecrease in vertical load on the inner front road wheel which is causedby lateral load shift is reliably suppressed. With such a configuration,a cornering force of the front road wheels 2 can be reliably increasedand hence, responsivity of turning behavior can be improved.

LIST OF REFERENCE SIGNS

1 vehicle

2 front road wheel

4 engine

6 steering wheel

8 steering wheel angle sensor

10 accelerator position sensor

12 vehicle speed sensor

14 PCM

16 basic target torque-deciding part

18 torque reduction amount-deciding part

20 final target torque-deciding part

22 engine control part

The invention claimed is:
 1. A vehicle behavior control device appliedto a vehicle having a steerable front road wheel and a driving deviceconfigured to drive a drive road wheel, the vehicle behavior controldevice comprising a processor configured to: acquire a steering speed ofthe vehicle; and when the steering speed becomes equal to or greaterthan a given threshold which is greater than zero; acquire a targetadditional deceleration to be added to the vehicle based on the steeringspeed; decide a reduction amount of a driving force which is requiredfor realizing the target additional deceleration; and reduce the drivingforce from the driving device based on the decided reduction amount soas to increase a vertical load on the front road wheel, wherein as thesteering speed increases, the target additional deceleration increases,and when the steering speed is smaller than the threshold, the targetadditional deceleration is maintained at a value that is equal to avalue when the vehicle is not turning.
 2. The vehicle behavior controldevice according to claim 1, wherein the processor is configured tostart to reduce the driving force of the vehicle when the steering speedbecomes equal to or greater than the threshold, so as to increase thevertical load on the front road wheel.
 3. The vehicle behavior controldevice according to claim 1, wherein, when the steering speed becomesequal to or greater than the threshold, the processor is configured toincrease the vertical load on the front road wheel, in synchronizationwith a lateral load shift of the front road wheel.
 4. The vehiclebehavior control device according to claim 1, wherein as the steeringspeed increases, the target additional deceleration increases and comescloser to an upper limit value of 0.5 m/s².
 5. The vehicle behaviorcontrol device according to claim 4, wherein, based on the targetadditional deceleration, the processor is configured to decide anadditional deceleration added to the vehicle under a condition that achange rate of the said additional deceleration is equal to or less than0.5 m/s³, and to decide the reduction amount of the driving force whichis required for realizing the decided additional deceleration.
 6. Thevehicle behavior control device according to claim 1, wherein, when thesteering speed is smaller than the threshold, the processor ends thereduction of the driving force before the steering speed becomes zero.7. The vehicle behavior control device according to claim 1, wherein thedriving device is an engine, the reduction amount of the driving forceis a torque reduction amount of an output torque of the engine requiredfor realizing the target additional deceleration, and the processor isconfigured to reduce the output torque from the engine based on thedecided torque reduction amount.